This error means that backup RE is not synchronized with master. Usually this is seen after a Junos upgrade, RE switchover or a configuration change.
You can run command "show task replication" multiple times on the master routing engine and see if any of the protocols is not synchronizing. If the Synchronization Status is not complete for all the protocols, we need to investigate further.
If the replication status is complete for all the protocols and no recent config/hardware change, junos upgrade, RE switcover was done, this could be a transient issue like backup RE closing the socket due to miss of keep-alive from master RE.
You can monitor at intervals if the error is seen everytime you issue the command. Then refer the log messages and show log mastership from both the routing engines to find any clue. If everything is fine then it is not urgent to reboot the RE, you can plan for it in any upcoming maintenanace window.
RE1 already reboot and it stil not resolve. Even RE0 also already reboot but still same. As per last suggestion from JTAC said need to reboot both RE at same time and it need outage. JTAC said have internal PR for this issue. Can somebody from juniper here can check that PR?